Conventionally, in the process of dry etching, CVD, or the like in semiconductor manufacturing processes, processing is performed while supplying a large amount of gas in order to perform the process at high speed. Generally, a turbo-molecular pump that is provided with a turbine blade section and a screw groove pump section housed inside a pump case is used in the evacuation of a process chamber in the process of dry etching, CVD, or the like. When discharging a large amount of gas by the turbo-molecular pump, frictional heat generated in moving blades (rotor blades) is transmitted from the moving blades to stator blades (stationary blades), spacers, and a base in this order, and then released into cooling water in a cooling pipe provided in the base.
However, when discharging a larger amount of gas, the temperature of a rotor that includes the moving blades may disadvantageously exceed an allowable temperature. When the temperature of the rotor exceeds the allowable temperature, the speed of expansion by creep becomes higher. As a result, in any place in the turbine blade section and the screw groove pump section, disadvantageously, the moving blades and the stator blades may make contact with each other or the rotor and a screw stator may make contact with each other within a shorter period than a designed life.
Further, in this kind of semiconductor manufacturing apparatus, a reaction product is generated in etching or CVD, and the reaction product is likely to be accumulated on the screw stator of the screw groove pump section. A gap between the screw stator and the rotor is extremely small. Therefore, when a reaction product is accumulated on the screw stator, the screw stator and the rotor may be stuck to each other. As a result, the rotor may not be able to start rotating.
Therefore, the invention described in Patent Literature 1 (JP 3930297 B1) is provided with a first cooling water passage which cools rotor blades by cooling a pump case and a device for regulating the temperature of a screw stator (a heater and a second cooling water passage). The first cooling water passage is provided on the outer peripheral surface of the pump case, and cools the pump case to thereby cool stationary blades housed inside the pump case. In this manner, by providing the first cooling water passage and the temperature regulator, the temperature of the rotor is reduced and the accumulation of a reaction product on the screw stator is suppressed.
However, along with an increase in the size of a wafer to be processed, the flow amount of gas that should be discharged by the turbo-molecular pump increases, and the amount of heat generated due to the discharge of gas also increases. Therefore, a method in which the pump case is cooled as described in Patent Literature 1 does not have enough cooling capacity to cool the stationary blades. Further, the temperature of the base to which the pump case is fixed becomes high by temperature regulation. Therefore, heat flowing to the pump case from the base is a factor that inhibits cooling of the stationary blades. Therefore, a turbo-molecular pump that has sufficient cooling capacity to cool stationary blades and can regulate the temperature so that the temperature of the screw stator is a reaction product accumulation prevention temperature is required. On the other hand, when a turbo-molecular pump has sufficient cooling capacity to cool the stationary blades and the sublimation temperature of a reaction product is higher than the cooling temperature, the reaction product may be accumulated on the inner side of a spacer that corresponds to the bottom step moving blade, and the bottom step moving blade may disadvantageously make contact with the reaction product.